Alternative theory for THC as protection from UV-B
Posted: Sat Jan 05, 2019 12:54 am
An old study from the 80's caused quite a stir when posted on cannabis forums as it reported that exposure to UV-B light caused a proportional increase in THC production. The author of the paper hypothesized that because THC was an excellent absorber of UV radiation, and increased proportionally in response to UV-B radiation, that it's evolved biological function was to act as a sort of sunblock to protect the plant from being damaged by UV radiation. Ever since people have been adding UV lights to their grows and it does seem to increase THC as well as terpenes, but that explanation has never sat right with me.
Why does every other plant get along just fine without THC to protect it from UV? Why does cannabis itself get along just fine without this "sunblock" up until the stage where it begins to reach sexual maturity? THC is not there to protect the plant from UV, it does not increase with exposure to UV to protect the plant, it is there to help gather pollen that has been released from male plants that is riding on the wind. THC is very sticky and it is no coincidence that its flowers (the plant's sex organs) are what's covered in it, not its leaves or its stems. When you rub pollen onto the flower, it pollinates the bud and causes seeds to form. The larger the flower is, the more seeds it can produce if exposed to pollen.
Now ask yourself, what would increase the chances that the flower in question will be exposed to pollen and be able to produce seeds through sexual reproduction? Well, if the pollen is borne on the wind, then obviously the exterior of the plant would have a much better chance of getting pollen to hit it than the interior of the plant because there is better airflow, additionally possible bud sites inside the plant don't get as much light so they wouldn't be able to photosynthsize as much and form as many seeds. Therefore, cannabis would have evolved over time to dedicate its resources to areas that have good exposure to both light and wind. This is what we see, the plant puts more resources into producing flowers and THC at the tops of the plant. Budsites that are exposed to air and light produce more flowers and THC than ones deprived of either.
Now where does UV come into all of this? Well, the spectrum of light can tell the plant a lot of information. For example, if a seedling is under the shade of another plant, the spectrum of light reaching it will be different than it would be if it were in direct sunlight. Green light can pass through the canopy better as it is reflected off of chlorophyll. Far red light also passes through better because it is not absorbed by chlorophyll. Therefore if the plant is getting lots of far red and green light, it knows that it is in shade and will stretch vertically to reach the sunlight. Lots of UV, red, and blue light on the other hand tells the plant that it is getting direct sunlight.
Red light is always able to reach the plant, no matter what angle the sun is at and how much atmosphere the light has to filter through, however the shorter wavelengths of blue and UV light are scattered when the sun is at an angle and the light has to travel through more atmosphere. Therefore the proportion of blue/UV light increases as the sun gets higher in the sky and the overall irradiance increases. Only when the sun is directly overhead is the plant exposed to UV, so the plant knows that anything that is exposed to UV is not shaded at midday when the sun's intensity is at its peak and the plant's rate of photosynthesis is at its peak. It knows that it is the top of the plant in other words and therefore has the best exposure to both light and (pollen bearing) wind. This means if my theory is correct the plant would put more resources into these buds because it knows that they will have the best chances to gather pollen and have the best light exposure to photosynthesize for the seeds.
People report that UV-B is not the only spectrum that causes increased production of THC and terpenes, UV-A and blue or violet light also reportedly work which would make sense as they would all tell the plant the same thing essentially, that the part of the plant being exposed to that spectrum of light is getting full sun during mid-day when the plant's rate of photosynthesis is at its peak.
Any thoughts?
Why does every other plant get along just fine without THC to protect it from UV? Why does cannabis itself get along just fine without this "sunblock" up until the stage where it begins to reach sexual maturity? THC is not there to protect the plant from UV, it does not increase with exposure to UV to protect the plant, it is there to help gather pollen that has been released from male plants that is riding on the wind. THC is very sticky and it is no coincidence that its flowers (the plant's sex organs) are what's covered in it, not its leaves or its stems. When you rub pollen onto the flower, it pollinates the bud and causes seeds to form. The larger the flower is, the more seeds it can produce if exposed to pollen.
Now ask yourself, what would increase the chances that the flower in question will be exposed to pollen and be able to produce seeds through sexual reproduction? Well, if the pollen is borne on the wind, then obviously the exterior of the plant would have a much better chance of getting pollen to hit it than the interior of the plant because there is better airflow, additionally possible bud sites inside the plant don't get as much light so they wouldn't be able to photosynthsize as much and form as many seeds. Therefore, cannabis would have evolved over time to dedicate its resources to areas that have good exposure to both light and wind. This is what we see, the plant puts more resources into producing flowers and THC at the tops of the plant. Budsites that are exposed to air and light produce more flowers and THC than ones deprived of either.
Now where does UV come into all of this? Well, the spectrum of light can tell the plant a lot of information. For example, if a seedling is under the shade of another plant, the spectrum of light reaching it will be different than it would be if it were in direct sunlight. Green light can pass through the canopy better as it is reflected off of chlorophyll. Far red light also passes through better because it is not absorbed by chlorophyll. Therefore if the plant is getting lots of far red and green light, it knows that it is in shade and will stretch vertically to reach the sunlight. Lots of UV, red, and blue light on the other hand tells the plant that it is getting direct sunlight.
Red light is always able to reach the plant, no matter what angle the sun is at and how much atmosphere the light has to filter through, however the shorter wavelengths of blue and UV light are scattered when the sun is at an angle and the light has to travel through more atmosphere. Therefore the proportion of blue/UV light increases as the sun gets higher in the sky and the overall irradiance increases. Only when the sun is directly overhead is the plant exposed to UV, so the plant knows that anything that is exposed to UV is not shaded at midday when the sun's intensity is at its peak and the plant's rate of photosynthesis is at its peak. It knows that it is the top of the plant in other words and therefore has the best exposure to both light and (pollen bearing) wind. This means if my theory is correct the plant would put more resources into these buds because it knows that they will have the best chances to gather pollen and have the best light exposure to photosynthesize for the seeds.
People report that UV-B is not the only spectrum that causes increased production of THC and terpenes, UV-A and blue or violet light also reportedly work which would make sense as they would all tell the plant the same thing essentially, that the part of the plant being exposed to that spectrum of light is getting full sun during mid-day when the plant's rate of photosynthesis is at its peak.
Any thoughts?